Same domain / subdomain can't be used in 2 locations
Additional domains can be deleted and used elsewhere but Primary domains can't be recycled as of now
This can happen due to a few reasons
There is a typo in your domain name [like in the example above]
In this scenario fixing the typo will resolve your issue
Your DNS changes haven't propagated yet
In this case you need to wait longer and try again after a few hours or the next day to see if it works
Your DNS configuration is not setup correctly
Please reach out to your Domain Provider and discuss the errors with their support team
Maybe you have conflicting (multiple) records for the same subdomain [for example if blog.mydomain.com has a CNAME record pointing to wp.msgsndr.com but it also has an A record pointing to some other provider]
In such cases removing the other duplicate record will fix your issue
Please make sure there are no additional AAA, TXT, records etc if you plan to use that slug / root domain for WordPress